The three-phase transformer core is both the magnetic circuit of the transformer and its mechanical skeleton, which is composed of a core and an iron yoke. The three-phase transformer core column is provided with windings, and the iron yoke connects the iron cores to form a closed magnetic circuit. In order to reduce the hysteresis loss and eddy current loss in the iron core, the iron core is generally laminated with a high magnetic permeability silicon steel sheet.

According to the structural form and process characteristics, the three-phase transformer core can be divided into two types: laminated type and involute type, and the laminated core can be divided into two types: core type and shell type. The three-phase transformer core of the shell structure is the top surface, the bottom surface and the side surface of the winding surrounded by the iron yoke. Due to the limitation of transportation, the large-capacity three-phase transformer needs to lower the core height, and a part of the upper and lower iron yokes of the ordinary three-phase chip transformer is moved to the outside of the two side columns.

The core structure of the three-phase transformer core is the iron yoke against the top and bottom surfaces of the winding, but does not surround the side of the winding, its mechanical strength is better, the structure is relatively simple, and the assembly and insulation of the winding are also easier. Therefore, the domestic power transformers all adopt a core structure.